An internal combustion engine is known from DE 101 47 536 A1, in which ah exhaust gas heat exchanger thermally connected to the exhaust gas system is provided in an intake system which may be activated or deactivated via control valves, designed as flaps. The exhaust gas heat exchanger may be bypassed on the intake system side as well as on the discharge system side by means of bypass lines.
Furthermore, a diesel engine is known from DE 103 47 834 A1 which has an exhaust gas aftertreatment device. The exhaust gas recirculation device comprises a dual-path system, a cooling device being provided in a first path, and the second path being connected in parallel to the first path. An intercooler is also provided in the charge air feed line.
An internal combustion engine having exhaust gas recirculation is known from DE 10 2004 021 386 A1, in which two heat exchangers are provided in an exhaust gas recirculation line. The exhaust gas flowing through the two heat exchangers is thus cooled. An additional heat exchanger is provided in a charge air line.
An internal combustion engine is also known from FR287 64 17, in which two heat exchangers are provided in series in an exhaust gas recirculation line. A three-way valve is respectively provided upstream from the first heat exchanger and between the two heat exchangers, a bypass branching off from each three-way valve. Depending on the load state of the internal combustion engine, the exhaust gas may be led through the two heat-exchangers or through the bypass. If the engine is under moderate load, the exhaust gas is led through the first heat exchanger and bypasses the second heat exchanger. In the known internal combustion engines and operating methods, the ability to cool the exhaust gas as needed is inadequate at best.
The object of the present invention, therefore, is to provide a method and an internal combustion engine by means of which a highly efficient reduction in nitrogen oxide emissions in a broader range of the characteristic map is possible while avoiding fouling of the coolers.